In certain gas turbine combustors, a plurality of openings is provided about a flow sleeve surrounding the combustor liner for injecting air in a generally radial direction through the flow sleeve into an annular passage radially between the flow sleeve and the combustor liner for impingement cooling the liner. The air is radially injected generally normal to a free stream of impingement cooling air flowing within the flow sleeve, originating in a similar axially-connected annular passage radially between a transition duct (which carries the combustion gases from the combustor liner to the turbine first stage) and a surrounding impingement sleeve. This redirected compressor discharge air mixes with fuel at the aft end of the combustor and the fuel/air mixture is then combusted within the liner.
The impingement cooling air injected in the radial direction through the flow sleeve openings and into the free stream has a momentum exchange with the axially flowing air and must be accelerated by the axially flowing free stream air until the cross flowing air reaches the free stream velocity. This process causes an undesirable pressure drop in the flow to the combustor. In order to reduce the pressure drop, the air supply configuration has been altered to introduce the compressor discharge air into the passage substantially in the same axial direction as the air already flowing in the stream. This arrangement, however, results in the injecting flow tending to be sucked onto the outer wall of the passage, i.e., the inner wall of the flow sleeve, a manifestation of the so-called Coanda effect which reduces cooling efficiency.
It would therefore be desirable to inject air other than radially into the flow sleeve passage, but in such a way that the Coanda effect is eliminated or at least minimized, and cooling of the liner is enhanced.